1. Field of the Invention
The present invention relates to an optical apparatus for projecting stationary images onto or from a relatively moving object such as a continuously moving film strip and more particularly to a multifacet reflecting roof polygon scanning system suitable for incorporation into projectors, cameras and optical scanning equipment to optically immobilize a moving image with relatively minimal distortion.
2. Description of the Prior Art
While the present invention is directed to a modular optical apparatus that can be incorporated as an essential component in a number of optical devices, reference will only be made herein to the field of motion pictures.
The conventional projection of motion pictures has required an intermittent-motion film transport mechanism. The conventional projector has traditionally produced objectionable noise, film wear, frame and screen registration errors and frame rate limitations. The noise that is typically created by the intermittent-motion projection system, has required a projection booth in a commercial environment. The required intermittent movement not only damages the perforations in the film but the continuous starting and stopping and flicker effects cause severe speed limitations. Frequently, the projected images appear to bounce due to vertical instability and flicker is still present in conventional equipment. Additionally, the intermittent-motion creates interfacing problems between the correlations of the sound and visual characteristics of the motion picture.
In one conventional projector, a three bladed shutter, wherein each blade has a 55.degree. sweep, will block a total of 165.degree. of a total of 360.degree. of illumination. In effect, this means that 46% of the time the screen is blackened due to the light loss related to the shutter affect. This reduces the apparent image illuminance correspondingly by 46%. In addition, the complicated structure of the intermittent-motion transport requires a complex interfacing of the film into the projector.
A conventional projector when utilized in a video converter application requires a compensator to immobilize the film frame on the screen for solving the synchronization problem associated with the normal projection rate of 24 frames per second of a motion picture film interfaced with the 30 fields per second scanning of the typical video system.
Various forms of optical compensating devices, have been suggested over the last 60 years. Optical compensators or image immobilizers have classically fallen under three separate categories; rotating and/or oscillating mirror devices, rotating lens devices and rotating polygon prism devices. The German built Mechau projector of U.S. Pat. No. 1,401,346 is a classical example of a mirror type of optical compensator. The Mechau projector was built in the 1920's and was apparently the first technically successful continuous projector.
The Alexanderson U.S. Pat. No. 1,937,378 and the Ripley et al U.S. Pat. No. 1,091,864 disclose relatively simple polygon reflecting projectors.
The Bauersfeld U.S. Pat. No. 1,154,835 discloses a reflector drum which has a reflector comprising three planar reflectors having perpendicular reflecting surfaces which are respectively lying along a Cartesian coordinate with a film window limiting the illumination of the film frame.
The Campbell U.S. Pat. No. 3,583,798 discloses a high speed camera incorporating an optical compensator comprising a centrally fixed mirror for directing a light ray outward to a reflective rhombic configuration.
The Miller U.S. Pat. No. 1,530,903, Barr U.S. Pat. No. 663,153 and U.S. Pat. No. 1,156,596 are cited of general interest.
The Thun German Pat. Nos. 547,240 and 563,520 are directed to a lenticular lens systems for high speed photography.
Rotating lens devices have been less successful than the mirror devices or other methods due to the aberration problems and the cost requirement for precision lenses.
Examples of the rotating prism optical compensators can be found in the Leventhal U.S. Pat. Nos. 2,085,594; 2,417,002 and Re22,960. The Tuttle U.S. Pat. No. 2,070,033, Eisler U.S. Pat. No. 2,262,136 and Husted U.S. Pat. No. 3,539,251 are other examples of prism optical compensators.
Optical immobilization can be described as a displacement of a light beam through the optical system in such a manner that the portion of the beam coming from the subject, in the case of a camera taking a picture, or the portion of a beam extending from the projector to the screen, in the case of a motion picture projection, is held rigidly stationary, centered at the optical axis of exposure or projection respectively, while the portion of the beam which is immediately adjacent the intersecting film, is optically displaced so as to move in synchronism with the movement of the film.
The use of a rotating solid polygonal prism can produce a refraction of a light beam as it enters the prism and again as it leaves the prism to offset or displace a section of the beam within the apparatus, while maintaining the displaced section parallel to the stationary portion of the beam. The displaced section of the light beam directly intersects the film with the displacement being of a progressive or frame lap dissolve nature such that the displacement portion of the beam continually moves in exact synchronism with the moving film.
A solid polygon having an appropriate refractive index can provide frame lap dissolve. The refractive index would have to be in the order of 2.0 and the corresponding aberration control would demand a minimum of 26 facets which implies a maximum relative aperture of approximately f/7. In realizable solid polygon systems a refractive index of approximately 2.0 cannot be achieved and each successive projected frame replaces its predecessor frame in a top to bottom "wiping" motion with an inherent flicker that requires a corrective shutter between the frames.
An optical compensator that was developed for the Philco Research Division for use as a motion picture film scanner for television transmission in the early 1950's recognized some of the problems of a solid polygon. The Kudar U.S. Pat. Nos. 2,972,280 and 2,860,542 described this work. Basically, the Kudar patents disclose a hollow polygon device which utilized a set of prisms located within a cylindrical cavity of the polygon to deviate the light beam sufficiently to permit a lap dissolved framing which was flicker free, required no shutter, achieved a moderate relative aperture, for a 24 facet system, while at the same time provided moderate control of optical aberrations and film shrinkage compensation. The Kudar devices as described in the patents were developed upon the theory that the parallelism of the stationary and displaced portions of the projected beam required, the beam to be refracted to the same extent upon entering and leaving the polygon prism. Some of the disadvantages of the Kudar system include a limitation of the relative aperture of the optical system, the requirement of expensive materials for the prisms, the existence of field curvature aberrations and other refractive optical aberrations which are particularly destructive in a projection system. The Kudar device however has been utilized as a color television film scanner as described in the paper, "New 35 mm Television Film Scanner" Journal of SMPTE, Vol. 62, January 1954, Page 45.
The Kirkham U.S. Pat. No. 2,817,995 suggests a modification of a hollow polygonal prism concept by the provision of a rotatable compensating core to permit adjustment for the film shrinkage.
The Korb U.S. Pat. No. 2,515,453 is cited of general interest to disclose a single pass prism optical compensator.
Some devices of the prior art are capable of providing flicker-free lap dissolve framing, no shuttering and film shrinkage adjustment. For example the Kudar device taught the extension of the optical path through the compensator and the compensation of film shrinkage by the various mounting of movable prisms within the hollow polygon. The result was accomplished with relatively expensive components and provided a limited relative aperture while introducing kinetic refractive aberrations.
Problems such as dynamic keystoning and ghost images still exist when applying prior art polygon reflective scanners to motion picture projectors and cameras. There is still a need to eliminate aberration problems while providing a maximum relative aperture to maximize the light efficiency of the system.